This invention relates to a turbocharger for marine engines.
One of the biggest factors limiting the power output of an internal combustion engine is its capacity to pump air into its cylinders. Combustible fuel needs the oxygen contained in air to create the combustion reaction. For a given amount of air pulled into a naturally aspirated internal combustion engine cylinder, only a certain amount of fuel can be burned efficiently. If more fuel is provided in the cylinder than necessary, it will be wasted unless more air is forced into the cylinder to support efficient combustion.
It is possible to force air into an engine cylinder by the process of supercharging. Supercharging is the process of compressing the fresh outside air before it enters the cylinders. By supercharging, a greater weight of air is available for efficient combustion of more fuel, thus producing a greater output from the same engine displacement.
There are two general methods of supercharging an internal combustion engine. In one case, a mechanically driven blower is used to compress the intake air before it enters the cylinder. Power to drive this blower is taken off the engine crank shaft usually through a gear train.
Another method of supercharging is to use a turbocharger. A turbocharger utilizes the energy in the exhaust gases coming from the cylinders to drive a compressor and compress the intake air. A turbocharger takes no power away from the crank shaft. In addition, a turbocharger utilizes energy in the exhaust gases that would otherwise be lost. Generally, the design of a turbocharger is mechanically more simple than a mechanical supercharger or blower. Bearing loads are less. Gear trains are eliminated.
Turbocharging not only increases the power output of an engine, but also causes better combustion efficiency which results in more energy from the fuel available for useful work. Due to better combustion, more of the fuel is burned and the exhaust gas is cleaner. Additionally, the turbocharger may act as a muffler since the turbine blades break up exhaust noise. The turbocharger is particularly useful in combination with engines operated at high altitudes since the air is less dense at such altitudes thereby decreasing the efficiency of a naturally aspirated engine. Finally, improved combustion eliminates soot accumulations that cause fire or discharge of sparks from the exhaust.
In the past, turbocharging or supercharging engines in land vehicles such as race cars and farm vehicles have been commonplace. On the other hand, providing supercharged air for internal combustion marine engines has not been a usual practice. However, Boating Magazine, in the July 1974 issue, included an article entitled the M&W Marine Turbocharger by John Delves and Larry Kean which disclosed the concept of using turbocharging techniques for marine engines. The article disclosed that power output and fuel economy both improved as a result of utilizing a turbocharger on a marine engine.
While the marine turbocharger unit disclosed in the article has proven to be a very useful device, improvements were sought. For example, marine engines are generally confined below the water line under conditions of limited access, high temperature and low air circulation. As a result, engines of this nature tend to run "hot". Methods and devices must, therefore, be devised to decrease operating temperatures of engine compartments without adversely affecting efficiency. The engine compartment temperature should be sufficiently low in order to prevent ignition of combustible fumes in the compartment.